25 research outputs found
Frozen light in periodic metamaterials
Wave propagation in spatially periodic media, such as photonic crystals, can
be qualitatively different from any uniform substance. The differences are
particularly pronounced when the electromagnetic wavelength is comparable to
the primitive translation of the periodic structure. In such a case, the
periodic medium cannot be assigned any meaningful refractive index. Still, such
features as negative refraction and/or opposite phase and group velocities for
certain directions of light propagation can be found in almost any photonic
crystal. The only reservation is that unlike hypothetical uniform left-handed
media, photonic crystals are essentially anisotropic at frequency range of
interest. Consider now a plane wave incident on a semi-infinite photonic
crystal. One can assume, for instance, that in the case of positive refraction,
the normal components of the group and the phase velocities of the transmitted
Bloch wave have the same sign, while in the case of negative refraction, those
components have opposite signs. What happens if the normal component of the
transmitted wave group velocity vanishes? Let us call it a "zero-refraction"
case. At first sight, zero normal component of the transmitted wave group
velocity implies total reflection of the incident wave. But we demonstrate that
total reflection is not the only possibility. Instead, the transmitted wave can
appear in the form of an abnormal grazing mode with huge amplitude and nearly
tangential group velocity. This spectacular phenomenon is extremely sensitive
to the frequency and direction of propagation of the incident plane wave. These
features can be very attractive in numerous applications, such as higher
harmonic generation and wave mixing, light amplification and lasing, highly
efficient superprizms, etc
Unidirectional Lasing Emerging from Frozen Light in Non-Reciprocal Cavities
We introduce a class of unidirectional lasing modes associated with the
frozen mode regime of non-reciprocal slow-wave structures. Such asymmetric
modes can only exist in cavities with broken time-reversal and space inversion
symmetries. Their lasing frequency coincides with a spectral stationary
inflection point of the underlying passive structure and is virtually
independent of its size. These unidirectional lasers can be indispensable
components of photonic integrated circuitry.Comment: 5 pages, 3 figure
Absorption suppression in photonic crystals
We study electromagnetic properties of periodic composite structures, such as
photonic crystals, involving lossy components. We show that in many cases a
properly designed periodic structure can dramatically suppress the losses
associated with the absorptive component, while preserving or even enhancing
its useful functionality. As an example, we consider magnetic photonic
crystals, in which the lossy magnetic component provides nonreciprocal Faraday
rotation. We show that the electromagnetic losses in the composite structure
can be reduced by up to two orders of magnitude, compared to those of the
uniform magnetic sample made of the same lossy magnetic material. Importantly,
the dramatic absorption reduction is not a resonance effect and occurs over a
broad frequency range covering a significant portion of photonic frequency
band
Waveguide photonic limiters based on topologically protected resonant modes
We propose a concept of chiral photonic limiters utilising topologically
protected localised midgap defect states in a photonic waveguide. The chiral
symmetry alleviates the effects of structural imperfections and guaranties a
high level of resonant transmission for low intensity radiation. At high
intensity, the light-induced absorption can suppress the localised modes, along
with the resonant transmission. In this case the entire photonic structure
becomes highly reflective within a broad frequency range, thus increasing
dramatically the damage threshold of the limiter. Here we demonstrate
experimentally the principle of operation of such photonic structures using a
waveguide consisting of coupled dielectric microwave resonators.Comment: 6 pages, 4 figure
Frozen light in periodic stacks of anisotropic layers
We consider a plane electromagnetic wave incident on a periodic stack of
dielectric layers. One of the alternating layers has an anisotropic refractive
index with an oblique orientation of the principal axis relative to the normal
to the layers. It was shown recently (A. Figotin and I. Vitebskiy, Phys. Rev.
E68, 036609 2003) that an obliquely incident light, upon entering such a
periodic stack, can be converted into an abnormal axially frozen mode with
drastically enhanced amplitude and zero normal component of the group velocity.
The stack reflectivity at this point can be very low, implying nearly total
conversion of the incident light into the frozen mode with huge energy density,
compared to that of the incident light. Supposedly, the frozen mode regime
requires strong birefringence in the anisotropic layers - by an order of
magnitude stronger than that available in common anisotropic dielectric
materials. In this paper we show how to overcome the above problem by
exploiting higher frequency bands of the photonic spectrum. We prove that a
robust frozen mode regime at optical wavelengths can be realized in stacks
composed of common anisotropic materials, such as YVO₄, LiNb,
CaCO₃, and the like.Comment: to be submitted to Phys. Rev.
Light-induced optical switching in an asymmetric metal-dielectric microcavity with phase-change material
We propose an infrared power switch based on an asymmetric high-Q microcavity
incorporating a metallic nanolayer in close proximity to a layer made of a
phase-change material (PCM). The microcavity is designed so that when the PCM
layer is in the low-temperature phase, the metallic nanolayer coincides with a
nodal plane of the resonant electric field component, to allow a high resonant
transmittance. As the light intensity exceeds a certain threshold,
light-induced heating of the PCM layer triggers the phase transition
accompanied by an abrupt change in its refractive index in the vicinity of the
transition temperature. The latter results in a shift of the nodal plane away
from the metallic nanolayer, rendering the entire microcavity highly reflective
over a broad frequency range. The nearly binary nature of the PCM refractive
index allows for the low-intensity resonant transmission over a broad range of
ambient temperatures below the transition point.Comment: 5 EPL pages, 4 figure